Sheet feeding device and image forming apparatus

ABSTRACT

A sheet feeding device having a conveyance roller to convey a sheet and a cleaning member in slide contact with the outer circumferential surface of the conveyance roller for removing foreign matter adhering to the conveyance roller, wherein the cleaning member is formed by a conductive brush, and an image forming apparatus having the sheet feeding device thereof.

This application is based on Japanese Patent Application No. 2006-070406 filed on Mar. 15, 2006, in Japanese Patent Office, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a sheet feeding device used for an image forming apparatus such as a copying machine, a printer, a facsimile machine and a multi function machine having the functions thereof, and in particular, to a sheet feeding device provided with a cleaning member to remove foreign matter such as paper dust adhering to an outer circumferential surface of a sheet feeding roller.

There has been a fixed type foreign matter removing device to remove the foreign matter like paper dust adhering to a surface of a roller member by slidingly contacting a fixed type cleaning member (flexible member such as brush, felt, PET sheet) onto the roller member such as a sheet feeding roller and a conveyance roller to convey a recording sheet.

An image forming apparatus of Patent document 1 has a foreign matter removing device in which a fixed type cleaning member like a felt is caused to be in contact with the conveyance roller so as to clean a surface of the recording sheet through the conveyance roller.

Also, there has been a rotation type foreign matter removing device to remove the foreign matter such as the paper dust adhering to the surface of the roller member such as the feeding roller and the conveyance roller by contacting a cleaning roller (brush and felt) with the roller member to convey the recording sheet.

An image forming apparatus in Patent document 2, wherein a cleaning roller to clean the recording sheet to be conveyed is cleaned by contacting a brush.

An image forming apparatus in Patent Document 3 uses a method, wherein the cleaning roller is in contact with the recording sheet to be conveyed.

A foreign matter removing device in Patent Document 4, wherein a rotating brush roller is in contact with the conveyance roller to clean the conveyance roller and a rotation roller is in contact with this brush roller to clean the brush roller and then a flexible sheet is in contact with the rotation roller to clean the rotation roller.

[Patent document 1] Non-examined publication No. 11-52641

[Patent document 2] Non-examined Publication No. 11-208918

[Patent document 3] Non-examined Publication No. 8-314344

[Patent document 4] Non-examined Publication No. 2004-224451

When a printed sheet, in particular, an offset sheet passes through a sheet feeding device or a sheet conveyance device provided in an image forming apparatus or a post-process apparatus, sprinkled powder, ink residue sticking on the sheet and coating agent on the sheet surface adhere to an outer circumferential surface of the sheet feeding roller and the conveyance roller, and deteriorate a transportability of the sheet feeding roller and the conveyance roller with the result that sheet transportation becomes unstable.

In the foreign matter removing devices where the fixed type cleaning member in contact with the aforesaid sheet feeding roller and the conveyance roller removes the foreign matter, the foreign matter accumulate in the cleaning member such as brush, foaming urethane, felt, moquette member and PET sheet, thus it becomes impossible to maintain cleaning performance for a long period of time and a failure of sheet conveyance will occur. Also, maintenance becomes necessary to replace the cleaning member.

In a reverse roller type sheet feeding roller method, a rising fabric member such as a moquette and a flexible member such as an urethane foam or a PET sheet are imposed on the roller to remove the foreign matter such as the paper dust adhering to rotation roller member such as a pick roller and the feeding roller. However, in the rising fabric member and the flexible member, since scraped foreign matter cannot be separated from the roller, cleaning effect cannot be sustained and cleaning members and rollers need to be cleaned or replaced periodically.

In the image forming apparatus of Patent Document 1, there was a problem in durability that the foreign matter such as the paper dust is accumulated in the cleaning member in short time, then the paper dust exceeding a cleaning capacity is conveyed to a transferring area.

In the rotation type foreign matter removing device wherein the cleaning roller like the rotation brush is in contact with the roller member such as the feeding roller and the conveyance roller, unless a rubber material of the roller member and a material of the cleaning roller are appropriate, the foreign matter such as the paper dust cannot be removed stably for a long period of time. Thus entering of the foreign matter into the transferring area cannot be reduced.

In the image forming apparatus of Patent Document 2, there was a problem that conveyance of a transfer material has an unstable factor because it is configured to have a speed difference between the cleaning roller and the transfer material.

In the image forming apparatus of Patent Document 3, there was a problem in durability that cleaning becomes not effective when the foreign matter such as the paper dust accumulates on the surface of the cleaning roller.

In the image forming apparatus of Patent Document 4, unless the material of the conveyance roller rubber and the cleaning member are selected appropriately, stable sheet conveyance performance and a high efficiency of cleaning cannot be obtained.

SUMMARY

The present invention is achieved by the followings.

1. A sheet feeding device, having a sheet conveyance roller to convey a sheet and a cleaning member in slide contact with an outer circumferential surface of the conveyance roller to scrape the surface thereof for removing foreign matter sticking on the conveyance roller; wherein the cleaning member is formed with conductive brush.

2. An image forming apparatus having the sheet feeding device of 1 and an image forming section to form an image on the sheet conveyed from the sheet feeding device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural view of an image forming apparatus composed of an image forming apparatus main body, a post-processing apparatus, a large capacity sheet feeding apparatus and an automatic document conveyance apparatus.

FIG. 2 is a structural view of an image forming apparatus related to the present invention.

FIG. 3 is a cross-sectional view of a first sheet feeding device of a sheet feeding cassette.

FIG. 4 is a cross-sectional view of a second sheet feeding device of the image forming apparatus main body.

FIG. 5 is a front view showing other embodiment of a sheet feeding apparatus.

FIG. 6 is a plane cross-sectional view of the sheet feeding apparatus.

FIG. 7 is a characteristic diagram showing changes of a friction coefficient of an outer circumferential surface of a conveyance roller.

FIG. 8 is a partial cross-sectional view of the conveyance roller.

FIG. 9 is a characteristic diagram indicating changes of a friction coefficient of a conductive brush resulting from elapsed number of sheets passing through.

FIG. 10 is a cross-sectional view indicating an amount of overlap between the cleaning member and the conveyance roller.

FIG. 11 is a characteristic diagram indicating a relation between the amount of overlap and a loading torque of the conveyance roller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Next, an image forming apparatus of the present invention is explained with reference to the drawings.

<Image Forming Apparatus>

FIG. 1 is a structural view of an image forming apparatus composed of image forming apparatus main body A, post-processing apparatus FS, large capacity sheet feeding apparatus FT and automatic document conveyance apparatus DF.

Image forming apparatus main body A is composed of image forming section 1, fixing device 9 and sheet conveyance system. Image forming section 1 is composed of charging device 3 provided in a peripheral area of image carrier 2, image exposing device 4, developing device 5, transferring device 6, discharging device 7A, separating claw 7B and cleaning device 8.

The sheet conveyance system has sheet feeding cassette 10, first sheet feeding device 11, second sheet feeding device (register roller) 12, conveyance device 13, sheet ejecting device 14, a first conveyance section having manual sheet feeding device 15, and circulating re-feeding section to circulate and re-feed sheet S.

Sheet feeding cassette 10 and first sheet feeding device 11 are formed with a plurality of sheet feeding devices (3 stories in the figure) to store and send various sizes of sheets S and. Sheet S sent out from sheet feeding device 20 of large capacity sheet feeding apparatus LT is fed to second sheet feeding device 12.

Document d placed on a document table of automatic document conveyance apparatus DF is conveyed through sheet feeding device 21 and an image in document d is read by an image scanning device.

In image forming section 1, processes such as charging, exposing, developing, transferring, separating and cleaning are conducted. On sheet S fed from sheet cassette 10, manual sheet feeding device 15 and large capacity sheet feeding apparatus LT, an image is transferred through transferring device 6. The image carried by Sheet S is fixed onto the sheet S through fixing device 9 and is ejected from sheet ejection device 14 to be sent to post-processing apparatus FS.

<Post-Processing Apparatus>

Post-processing apparatus FS is composed of entrance conveyance section 30, shift unit 31, stacker unit 32, staple unit 33 coversheet feeding device 34 and a sheet ejection section.

Coversheet K fed from coversheet feeding device 34 is conveyed through a conveyance roller group to be stored in stacker unit 32. Coversheet K is lapped over a plurality of sheets S to form front cover and rear cover. Meanwhile, coversheet K can be an inserter sheet to be inserted between the plurality of sheets S.

When a predetermined number of sheets S are loaded on stacker unit 32 and aligned, staple unit 33 staples sheet S at two positions or one position of a corner to bind sheets S and a booklet is made.

Sheets S after binding are nipped and conveyed by sheet ejection device 35 then ejected onto main tray 36 to be piled up.

<Sheet Feeding Device>

A sheet feeding device is applicable to first sheet feeding device 11 and second sheet feeding device 12 of sheet feeding cassette 10 disposed in image forming apparatus main body A, manual sheet feeding device 15, sheet feeding device 20 of large capacity sheet feeding apparatus LT, sheet feeding device 21 of automatic document conveyance apparatus DF and coversheet feeding device 34 of post-processing apparatus FS.

FIG. 2 is a structural view of other image forming apparatus related to the present invention. Meanwhile, parts having the same function as in FIG. 1 have the same symbols. Here, different points from FIG. 1 are explained.

Image forming apparatus A is called a tandem type color image forming apparatus having a plurality of sets of image forming sections 1Y, 1M, 1C, 1K, belt-shaped intermediate transfer substance 7, sheet feeding device and fixing device 9.

Image forming section 1Y to form yellow (Y) color image has charging device 3Y, image exposing device 4Y, developing device 5Y and cleaning device 8Y, which are arranged in a peripheral area of image carrier 2Y. Image forming section 1M to form magenta (M) color image has image carrier 2M, charging device 3M, image exposing device 4M, developing device 5M and cleaning device 8M. Image forming section 1C to form cyan (C) color image has image carrier 2C, charging device 3C, image exposing device 4C, developing device 5C and cleaning device 8C. Image forming section 1K to form black (K) color image has image carrier 2K, charging device 3K, image exposing device 4K, developing device 5K and cleaning device 8K.

Intermediate transfer substance 7 trains about a plurality of rollers and is supported to be able to rotate.

Each color image formed through image forming sections 1Y, 1M, 1C and 1K is consecutively transferred onto rotating intermediate transfer substance 7 through first transfer device 6Y, 6M, 6C and 6K to form a combined color image.

Sheet S stored in feeding cassette 10 of the feeding device is fed by first sheet feeding device 11 and passes through second sheet feeding device 12 then is conveyed to second transfer device 6A and then a color image is transferred onto the sheet S.

Sheet S on which the color image is transferred is pinched then heated and pressed by fixing device 9 to fix the color toner image (or toner image) on sheet S and then pinched by ejection device 14 to be ejected.

On the other hand, after the color image is transferred onto sheet S by second transfer device 6A, cleaning device 8A removes the remaining toner from intermediate transfer substance 7 from which sheet S is separated by curvature.

FIG. 3 is a cross sectional view of first sheet feeding device 11. Meanwhile, since manual feeding device 15, sheet feeding device 20 of large capacity sheet feeding apparatus LT, sheet feeding device 21 of automatic document feeding apparatus DF and coversheet feeding device 34 of post-processing apparatus FS have the almost the same structure as first sheet feeding device 11, first sheet feeding device 11 will be explained as a representative below.

Sheet S loaded on hoisting bottom plate 101 is elevated through hoisting member 102 by an unillustrated motor. When sheet S reaches at a position where the outer circumferential surface of pickup roller (conveyance roller) 111 comes in slide contact with a top surface of sheet S, the top surface of sheet S is detected by an unillustrated sensor and hoisting bottom plate 101 stops to lift.

At this sheet upper limit position, predetermined pressure P1 is imposed by own weight of pickup roller 111 and holder 114.

Pickup roller 111 and sheet feeding roller (conveyance roller) 112 start to rotate with a sheet feeding signal. Pickup roller 111 imposing the top surface of sheet S at predetermined pressure P1 is released from the sheet surface, after sheets S is conveyed to a nip position between sheet feeding roller 112 and double feeding prevention roller (reverse roller) 113.

Double feeding preventing roller 113 is driven in a reverse direction of a conveyance direction of sheet S through an unillustrated torque limiter and imposed on sheet feeding roller 112 by an unillustrated spring at predetermined pressure P2.

When double feeding preventing roller 113 comes in contact directly with sheet feeding roller 112, because sheet S does not exist in the nip position or when one piece of sheet S is fed into the nip position, the torque limiter slips beyond its limiting torque and double feeding preventing roller 113 rotates in accordance with the rotation of sheet feeding roller 112 to convey one piece of sheet S.

However, in case two pieces or more sheets S are conveyed into the nip position, the limit torque overcomes a friction force between the sheets, and double feeding prevention roller 113 rotates in the reverse direction to push back sheets S locating beneath top sheet S to prevent double feeding, thus one piece of sheet S can be conveyed.

At a down stream side of a separating roller pair composed of feeding roller 112 and double feeding prevention roller 113 in the sheet feeding direction, a pair of conveyance rollers 117 composed of drive roller 117A and driven roller 117B are arranged. The pair of conveyance rollers 117 nip one sheet S conveyed from the separating roller pair and conveys it to second sheet feeding device 12 shown in FIG. 1.

Above pickup roller 111, a cleaning member (cleaning brush) 116A fixed at an end of supporting plate 115 is arranged. Above feeding roller 112, a cleaning member (cleaning brush) 116B fixed at the other end of supporting plate 115 is arranged.

Cleaning member 116A scrapes against the outer circumferential surface of pickup roller 111 to scrape away the foreign matter adhering to the outer circumferential surface of pickup roller 111. Cleaning member 116B scrapes against the outer circumferential of feeding roller 112 to scrape away the foreign matter adhering to the outer circumferential surface of feeding roller 112.

Above drive roller 117A, cleaning member (cleaning brush) 116C is arranged. Cleaning member 116C scrapes against outer circumferential surface to remove the foreign matter adhering to the outer circumferential surface of drive roller 117A.

Cleaning member 116A, 116B and 116C are formed with conductive brushes. Characteristics and specifications of the conductive brush will be described later. Characteristics and specifications of pickup roller 111, sheet feeding roller 11, double feeding prevention roller 113 and drive roller 117A will also be described later.

FIG. 4 is a cross-sectional view of a conveyance device of second sheet feeding device 12 of image forming apparatus main body A shown in FIG. 1.

Second sheet feeding device 12 has drive roller (conveyance roller) 121 and driven roller 122 to pinch and convey sheet S, first cleaning member 123 composed of a cleaning brush to rotates and scrapes against drive roller 121, second cleaning member 124 to rotate and scrape against first cleaning member 123, and flexible third cleaning member 125 in slide contact with the outer circumferential surface of second cleaning member 124.

Drive roller 121 rotates in a clockwise direction, first cleaning member (hereinafter called cleaning brush) 123 is rotated in an anticlockwise direction by an unillustrated driving device and second cleaning member 124 is rotated by an unillustrated driving device in a clockwise direction. Third cleaning member 125 is imposed on the outer circumferential surface of second cleaning member 124 in a counter direction of rotation.

Cleaning brush 123 is formed with a conductive brush. Characteristics and specifications of the conductive brush will be described later. Characteristics and specification of drive roller 121 also described later.

FIG. 5 is a front cross-sectional view showing another embodiment of the sheet feeding device. FIG. 5 (a) shows a status before sheet feeding and FIG. 5(b) shows a condition during sheet feeding.

Meanwhile, parts having the same function as in FIG. 3 are represented by the same symbols and explanation of the parts thereof is omitted.

When a feeding start signal is inputted, pickup roller 111 swings centering on a rotation axis of sheet feeding roller 112 to come to contact with the upper surface of sheet S by its own weight. At the same time, an electric clutch CL explained later engages with rotate feeding roller 112, and pickup roller 111 starts to rotate through an unillustrated transmission device like a belt.

Sheet S is fed by rotation of pickup roller 111 and conveyed to the nip position where feeding roller 112 and double feeding prevention roller 113 are imposed each other, then sheet S is separated one by one and reaches to a pair of conveyance rollers 117 (see FIG. 3) in a downstream side of the conveyance direction.

When an unillustrated sensor detects that sheet S reaches to the pair of conveyance roller 117, electric clutch CL is disengaged then sheets S is withdrawn from nip position where feeding roller 112 and double feeding roller 113 are imposed each other and conveyed by pinching conveyance of the pair of conveyance rollers.

In first sheet feeding device 11, there are provided first cleaning member (hereinafter called cleaning brush) 118A, second cleaning member 118B, third cleaning member 118C and shielding member 118D above a space where pickup roller 111 and sheet feeding roller 112 opposes each other.

Cleaning brush 118A is composed of a cleaning brush, which rotates and scrapes against the outer circumferential surface of feeding roller 111. Cleaning brush 118A rotates in the anticlockwise direction by a drive device described later. Cleaning brush 118A and pickup roller 111 rotates in the same direction at a scraping position having a speed difference. Cleaning brush 118A and sheet feeding roller 112 rotate in the same direction at the scraping position having a speed difference.

Cleaning brush 118A removes paper dust and foreign matter by scraping pickup roller 111 and sheet feeding roller 112.

Second cleaning member 118B is a rotation roller to be rotated by a drive device and scrapes against cleaning brush 118A. Second cleaning member 118B removes the paper dust and the foreign matter adhering to cleaning brush 118A to refresh it.

Third cleaning member 118C is formed by a flexible thin plate, for example, such as PET (polyethylene terephthalate) in contact with an outer circumferential surface of second cleaning member 118B. An edge section of third cleaning member 118C is imposed on the outer circumferential surface of second cleaning member 118B in a counter direction of a rotation direction of second cleaning member 118B. Third cleaning member 118C removes the paper dust and the foreign matter adhering to second cleaning member 118B and shields a space above pickup roller 111.

Shielding member 118D, which is a thin flexible plate formed by, for example, PET (polyethylene terephthalate) or urethane sheet, is arranged in a symmetrical position to third cleaning member 118C, being in contact with the circumferential surface of second cleaning member 118B. The edge section of shield member 118D lightly is imposed on the outer circumferential surface of second cleaning member 118D in a trailing direction. Shield member 118D removes the paper dust and the foreign matter adhering to second cleaning member 118B and shields a space above sheet feeding roller 112.

In first sheet feeding device 11, when sheet S failed to be conveyed is removed, pickup roller 111 is lifted and swings upward centering on a sheet feeding roller axis. At this stage, since the space above cleaning brush 118A is shielded by third cleaning member 118C and shield member 118D, the paper dust and the foreign matter around second cleaning member 118B are prevented from exsorption.

Cleaning brush 118A is formed with a conductive brush. Characteristics and specifications of the brush will be explained later. Characteristics and specifications of pickup roller 111, sheet feeding roller 112 and double feeding prevention roller 113 are explained later.

Embodiment

Image forming apparatus main body A: Digital multi function machine bizhub7085™ (registered trade name by Konicaminolta) modified.

Pickup roller 111, sheet feeding roller 112 and double feeding prevention roller 113: hardness of rubber 56°, ether type urethane rubber, outer diameter 32 mm, rubber thickness 4 mm having embossing formed by asperities of 30 to 50 μm on a surface. The rubber hardness is indicated by a durometer, type A spring type hardness meter prescribed by ISO 7619 (JIS K6253).

Since silicone rubber has merits that rubber hardness can be soft, the rubber material itself do not tend to accumulate the dust and the roller surface can be roughen to increase a friction coefficient, it is used widely for roller material. On the other hand, since it has demerits that it is not durable against rubbing and is easy to be worn out, and an initial friction coefficient is low, an urethane rubber is more favorable than the silicone rubber as a material for rollers.

AS a representative of the cleaning member, cleaning brush 118A is explained below.

The specifications of the brush are as follows Dimensions Material of bristle Conductive acryl Thickness of bristle 6.25 denier (1 denier means a thickness of fiber where 450 m in length and 50 mg in weight) Density of bristle 100,000 pcs./25.4 mm² Outer Diameter of brush 16 mm Length of bristle  4 mm Overlap Between pickup roller 111 0.5 to 1.5 mm and cleaning brush 116 Between feeding roller 112 0.5 to 1.5 mm and cleaning brush 116

<Hardness of Rubber>

FIG. 7 is a characteristic diagram indicating results of measurement of change in a friction coefficient of the outer circumferential surface of pickup roller 111 and sheet feeding roller 112 resulting from the number of sheets passed. Offset printed sheets are used as the sheets.

As the rollers, (a) EPDM rubber (ethylene propylene rubber), (rubber hardness 35°) (b) urethane rubber (rubber hardness 75°), (c) urethane rubber (rubber hardness 56°), (d) urethane rubber (rubber hardness 44°) and (e) urethane rubber (rubber hardness 35°) are compared and studied. (f) means a lower limit of conveyance performance. TABLE 1 Friction coefficient (μ) of conveyance roller (a) (b) (c) (d) (e) (f) Start 1.68 1.28 1.52 1.62 1.37 1 After 1.49 1.20 1.40 1.55 1.27 1 200 pcs. After 1.09 1.24 1.32 1.53 1.22 1 300 pcs. After 1.06 1.24 1.33 1.52 1.15 1 900 pcs. After 0.96 1.26 1.38 1.50 0.94 1 1500 pcs. After — 1.23 1.33 1.45 0.86 1 2000 pcs. After — 1.08 1.34 1.48 0.90 1 3000 pcs. After — 1.12 1.34 1.44 0.92 1 5000 pcs. After — 1.11 1.25 1.40 1.01 1 7000 pcs. After — 1.11 1.29 1.43 1.00 1 9000 pcs. Note: (a): EPDM rubber (ethylene propylene rubber) (rubber hardness 35°) (b): Urethane rubber (rubber hardness 75°) (c) : Urethane rubber (rubber hardness 56°) (d): Urethane rubber (rubber hardness 44°) (e): Urethane rubber (rubber hardness 35°) (f): Lower limit of conveyance performance

Table 1 is data of experiment showing changes of friction coefficients of rollers in accordance with number of print sheets which is pinched and conveyed by the rollers formed with various kinds of rubbers.

According to the experience, both (c) urethane rubber (rubber hardness 56°) and (d) urethane rubber (rubber hardness 44°) have the friction coefficient μ of more than 1.25 and the rollers obtained a stable conveyance performance.

EPDM rubber roller (a) having low rubber hardness has high performance of sheet conveyance at initial stage of printing, however in case of an offset print sheet is conveyed, sprinkled powder, paper dust and ink residue adhering to sheet S are transferred onto the roller surface and they become difficult to be removed then a durability of sheet conveyance performance is decreased.

The roller formed by (b) urethane rubber (rubber hardness 75°) having a low friction coefficient due to high hardness of the rubber causes slip and sheet conveyance performance decreases.

The roller formed with (e) urethane rubber (rubber hardness 35°) has a preferable sheet conveyance performance at initial stage of use due to the high friction coefficient, however after 1000 pieces of sheet conveyance, the friction coefficient decreases and slip is caused and then the sheet conveyance performance decreases.

According to the above results, the rollers formed with poly ether type urethane rubber (a), (b) and (c) have preferable sheet conveyance performance.

Also in a condition where a roller surface is tainted by sprinkled powder, paper dust, and ink residue, the more the surface roughness Rz (an average roughness of 10 points) increases, the higher friction coefficient can be obtained.

In order to make the roller surface rougher, there are two methods, i.e. (1) a method to grind the roller surface and (2) a method where a roller forming surface of a roller forming metal die is roughen by embossing. In case of EDPM rubber rollers and silicone rubber rollers, method (1) is still capable of forming rough surface. In case of urethane rubber rollers, method (2) can make a rougher surface than method (1).

FIG. 8 is a partial cross-sectional view of a conveyance roller.

In case of pickup roller, it is effective that from 20 to 30 grooves having depth of 0.1 to 0.5 mm and width of 0.5 mm are formed on a circumference of the roller. However, in case of feeding rollers and double feeding prevention rollers, it will cause a bias wear, and no groove is preferred.

<Cleaning Member>

If the brush of cleaning member to clean the conveyance roller surface by scraping against sheet conveyance rubber rollers is not conductive, the surface of the rubber roller is charged and the paper dust and the foreign matter adhering to the surface of sheet conveyance rubber roller becomes difficult to be removed, and the surface of the sheet is also charged, and then a problem that a failure of image transfer in a transferring section of image forming apparatus A is caused occurs. Therefore the brush for cleaning is given the conductivity.

Brush 118A to clean pickup roller 111 and sheet feeding roller 112 is particularly needed to be small. However, there is a limit in size. A metal core where raised brushes are winded has to have an outer diameter of at least 6 mm for strength and the outer diameter of 8 mm is preferred to exert a stable cleaning function.

Regarding the bristle of cleaning brush 118A, a length of not less that 3 mm is needed. Thus adding the diameter of the metal core and the length of the bristle, the outer diameter of cleaning brush 118A has to be not less than 14 mm.

FIG. 9 is a characteristic diagram indicating results of measurement of change in a friction coefficient of the conductive brush in respect to a conductive brush of cleaning brush 118A in accordance with elapsed numbers of sheets passed.

Conductive brush (a) has the following dimensions:

Thickness of bristle: 6.25 denier

Density of bristle: 100,000 pieces per 25.4 mm²

Outer diameter: 16 mm

Length of bristle: 4 mm

Conductive brush (b) has the following dimensions:

Thickness of bristle: 15 denier

Density of bristle: 60,000 pieces per 25.4 mm²

Outer diameter: 16 mm

Length of bristle: 4 mm

(c) means a lower limit of conveyance performance.

In a conductive brush having a thickness of bristle 3 denier and a density of bristle 200000 per square inch (one inch is 25.4 mm), a torque loaded onto the conveyance roller is large and the conveyance rollers in the downstream side of first sheet feeding device 11 causes failures. TABLE 2 Friction coefficient (μ) of urethane rubber roller 56° (a) (b) Thickness of the Thickness of the bristle: 6.25 denier bristle: 15 denier Density of the Density of the Lower limit bristle: bristle: of 100,000/25.4 mm² 60,000/25.4 mm² performance Start 1.52 1.52 1 After 1.33 1.09 1 900 pcs. After 1.34 0.85 1 2000 pcs. After 1.34 — 1 3000 pcs. After 1.34 — 1 5000 pcs. After 1.25 — 1 7000 pcs. After 1.29 9000 pcs.

Table 2 is data of an experiment showing changes of friction coefficients of rollers in accordance with number of print sheets which is conveyed by the cleaning brush 118A formed with the aforesaid various kinds of conductive brushes and the rollers formed with urethane rubber (rubber hardness: 56°).

According to the results of the experience, conductive brush (a) with bristle thickness of 6.25 denier and bristle density of 100,000/25.4 mm², has less decrease of the friction coefficient μ due to the elapsed number of printing sheet processed and a stable sheet conveyance force of roller.

Contrary to it, in conductive brush (b) with bristle thickness of 15 denier and bristle density of 60,000/25.4 mm², the friction coefficient μ remarkably decreases due to the elapsed number of printing sheet passed and the sheet conveyance performance of roller decreases at about 2,000 pcs.

<An Overlapping Amount Between the Cleaning Member and the Conveyance Roller>

FIG. 10 is a cross-sectional view showing an overlapping amount between the cleaning member and the conveyance roller.

FIG. 11 is a characteristic diagram showing a relationship between the loading torque and overlapping amount at a position where the cleaning member and the conveyance roller are in contact each other.

<Upper Limit of the Overlapping Amount>

The more overlapping amount increases, the more an efficiency to scrape off the paper dust and the foreign matter adhering to the conveyance roller is improved.

After leaving cleaning brush 118A for 100 hours, under the condition where the overlapping amount is 2 mm, temperature is 30° C. and humidity is 80%, a change of outer diameter of cleaning brush 118A is measured. As the result, bristles of the brush is deformed from an initial outer diameter of 16 mm to 15.5 mm, thus the overlapping amount is changed from 2 mm to 1.5 mm. Consequently, an upper limit of the overlapping amount is 1.5 mm in cleaning brush 118A with bristle length of 4 mm. Meanwhile, it is obvious that the longer bristle, the more overlapping amount.

Though the overlapping amount is more than 1.5 mm, the bristle of the brush lies down and the overlapping amount decreases. If the overlapping amount changes from initial one, stable cleaning performance cannot be obtained. Thus, the upper limit of overlapping amount is preferred to be not more than 1.5 mm.

The change of length of the bristle is predicted as follow:

When the length of bristle is 3 mm and a maximum overlapping amount is 1.5 mm, since a limit of overlapping amount is proportional to the length of the bristle, the limit of overlapping amount is predicted as: 1.5 mm×(3 mm/4 mm)=1.1 mm. When the length of bristle is 2 mm and a maximum overlapping amount is 1.5 mm, the limit of overlapping amount is predicted as: 1.5 mm×(2 mm/4 mm)=0.75 mm.

<Lower Limit of Overlapping Amount>

FIG. 11 shows a result of measurements of loading torque of the conveyance roller which represents cleaning ability of cleaning brush 118A to scrape away the paper dust and the foreign matter.

At overlapping amount of 0.3 mm, the loading torque is 5 gfcm, which is almost 0. At overlapping amount of 0.5 mm, the loading torque is 50 gfcm, which is the lowest value of a desired loading torque. Thereby, the overlapping amount is needed to be set in between the lowest value of 0.5 and the highest value of 1.5 mm.

Meanwhile, in the present embodiment, while conductive acrylic material is used as the conductive brush, the present invention is not limited to the acrylic material. For example, conductive polyester material can be used. In case the conductive polyester material is used, it is predicted that durability is improved compared to the case of using conductive acrylic material. In the embodiment of the present invention, while post-processing apparatuses having a side stitch function has been explained as post-processing apparatuses connected to the image forming apparatus main body A, applications of the post-processing apparatus of the present invention for the image forming system is not limited to the applications, it is also applicable to post-processing apparatus such as gumming bookbinding machines, edge cutting machines, glued-on cover casing-in machines and cast sealing machines and image forming systems to which a plurality of these post-processing apparatuses are connected.

Also, in the embodiment of the present invention, while a post-processing apparatus connected to a copying machine has been explained, it is also applicable to image forming systems connected to image forming apparatuses such as shortrun printers, printers, facsimile machines and multi function machines.

According to the above embodiments, it is possible to provide a foreign matter removing device in which the foreign matter such as paper dust can be removed for a long period of time, entering of the foreign matter into the transfer area is reduced and a preferable image quality is obtained, and an image forming apparatus using the foreign matter removing device thereof.

Further, there are obtained effects that cleaning effect and durability of the feeding rollers and conveyance rollers are improved, conveyance performance of a sheet with more paper powder is improved and conveyance performance of an offset printed sheet, in particular, for an offset printed coated sheet is improved. 

1. A sheet feeding device, comprising: a conveyance roller to convey a sheet; and a cleaning member in slide contact with an outer circumferential surface of the conveyance roller to remove foreign matter adhering to the conveyance roller; wherein the cleaning member is formed with a conductive brush.
 2. The sheet feeding device of claim 1, wherein the outer circumferential surface of the conveyance roller is formed with urethane rubber.
 3. The sheet feeding device of claim 1, wherein the outer circumferential surface of the conveyance roller is formed with urethane rubber having a hardness of 40° to 60°.
 4. The sheet feeding device of claim 1, wherein the outer circumferential surface of the conveyance roller has a plurality of projections forming asperity.
 5. The sheet feeding device of claim 1, wherein a thickness of bristles of the conductive brush is from 5 to 10 denier.
 6. The sheet feeding device of claim 1, wherein an amount of overlapping between an end of a bristle of the conductive brush and the outer circumferential surface of the conveyance roller at a position in which the conductive brush and the conveyance roller press each other is from 0.5 mm to 1.5 mm.
 7. The sheet feeding device of claim 1, wherein the cleaning member is a rotation brush, which is rotated by a driving source.
 8. An image forming apparatus, comprising: the sheet feeding device of claim 1; and an image forming section to form an image on a sheet conveyed from the sheet feeding device. 